Razvoj mikrostrukture v deformirani nikljevi zlitini 625

Malej, Simon (author), Godec, Matjaž (mentor), Medved, Jože (comentor)

Glavni cilj doktorske disertacije je raziskava vpliva deformacije in toplotne obdelave na izločanje sekundarnih faz nikljeve zlitine 625 z različno kemijsko sestavo. V vroče deformiranih ploščah, ki imajo pozitivne segregacije z niobijem smo opazovali izločanje sekundarnih faz po staranju na temperaturi 750 °C. Ker se je povprečni delež niobija spreminjal čez segregacijski pas, smo spremljali izločanje sekundarnih faz pri različnem povprečnem deležu niobija. Pri majhnem povprečnem deležu niobija (< 4 mas.% Nb) so deformirana zrna omogočala izločanje večjega števila izločkov ?'' (Ni3Nb). Nasprotno, v rekristaliziranih zrnih je bila gostota izločkov ?''-faze veliko manjša, izločali pa so se samo na dvojčkih in drsnih linijah. Z večjim delež niobija (> 4 mas.% Nb) je izločanje večjega števila finih izločkov ?'' potekalo v deformiranih in rekristaliziranih zrnih. Na deformacijskem dilatometru smo spreminjali temperaturo deformacije in jo povezali z izločanjem ?''-faze s pomočjo EBSD-analiz. Temperatura deformacije (950, 1050 in 1150 °C) ima vpliv na porazdelitev faze ?'' in je povezana z lokalno razliko v orientaciji. V zadnjem delu disertacije smo raziskovali vpliv žarjenih in deformiranih vzorcev na utrjevanje z izločanjem ?'' v homogeniziranih ploščah z različnim dodatkom titana in aluminija. Na osnovi meritev trdot in mikrostrukturnih preiskav, ima dodatek titana (0,36 mas.%) in aluminija (0,35 mas.%) majhen vpliv na izločanje ?'' faze. Trdota deformiranih vzorcev se je po staranju na temperaturah 700 in 750 °C zaradi izločanja ?'', bolj povečala v primerjavi z žarjenimi vzorci. Majhno povečanje v natezni trdnosti pa je bilo povezano z deležem niobija (~ 3,3 mas%).

• Language: Slovenian
• Keywords: Inconel 625, segregacije, vroča deformacija, modifikacija s Ti in Al, staranje
• Work type: Doctoral dissertation
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2019
• PID: 20.500.12556/RUL-111489
• COBISS.SI-ID: 1844063
• Publication date in RUL: 02.10.2019

Secondary language

• Language: English
• Title: Microstructure development in deformed nickel alloy 625

Abstract

The main objective of doctoral thesis was to research the influence of the deformation and heat treatment on the precipitation of secondary phases in chemically modified Inconel 625. The precipitation of secondary phases during aging at 750°C was researched in hot rolled plates containing positive segregations with niobium. Due to segregations the fraction of niobium changed acros the segregation band. The deformed grains enabled precipitation of large number of fine ?'' (Ni3Nb) precipitates when fraction of niobium was low (< 4 wt.%). The opposite was observed in recrystalized grains where only a small number of ?'' precipitates was observed on twins and glide planes. The precipitation of large number of fine precipitates ?'' takes place in deformed as well as recrystallized grains when niobium content was high (> 4 wt.%). The precipitation of ?'' in samples hot compressed at different temperature was researched with EBSD-analyis. The local change in orientation of hot-deformed samples at different temperature (950, 1050 in 1150°C) had influence on the distribution of the ?''-phase. In the last part the influence of deformed and annealed samples was researched, on precipitation hardening by ?'' in homogenized plates with different addition of titanium and aluminium. The increased content of aluminium (0,36 wt.%) and titanium (0,35 wt. %) had small influence on the precipitation of the ?''. The hardness of deformed plates after aging at 700 and 750°C increased more than in annealed plates. Small increase in tensile strength was conected with low content of niobium (~ 3,3 wt.%).

• Keywords: Inconel 625, segregation, hot deformation, modification with Ti in Al, aging